diff --git a/install_and_cache_pkgs.sh b/install_and_cache_pkgs.sh
index bbf54dc..e4f6c2c 100755
--- a/install_and_cache_pkgs.sh
+++ b/install_and_cache_pkgs.sh
@@ -3,49 +3,66 @@
 # Fail on any error.
 set -e
 
+# Include library.
+script_dir="$(dirname -- "$(realpath -- "${0}")")"
+source "${script_dir}/lib.sh"
+
 # Directory that holds the cached packages.
 cache_dir=$1
 
 # List of the packages to use.
-packages="${@:2}"
+input_packages="${@:2}"
 
-package_count=$(echo $packages | wc -w)
-echo "Clean installing and caching $package_count package(s)."
+# Trim commas, excess spaces, and sort.
+packages="$(normalize_package_list "${input_packages}")"
+
+package_count=$(echo "${packages}" | wc -w)
+echo "Clean installing and caching ${package_count} package(s)."
 echo "Package list:"
-for package in $packages; do
-  echo "- $package"
+for package in "${packages}"; do
+  echo "- ${package}"
 done
 
 echo -n "Updating APT package list..."
 sudo apt-get update > /dev/null
 echo "done."
 
-echo "Clean installing and caching $(echo $packages | wc -w) packages..."
-for package in $packages; do
-  cache_filepath=$cache_dir/$package.tar.gz
+manifest=""
+echo "Clean installing and caching ${package_count} packages..."
+for package in "${packages}"; do
+  get_package_name_ver "${package}" # -> package_name, package_ver
+  package_deps="$(apt-get install --dry-run --yes "${package_name}" | grep "^Inst" | awk '{print $2}')"
 
-  echo "- $package"
-  echo -n "  Installing..."
-  sudo apt-get --yes install $package > /dev/null
+  echo "- ${package_name}"
+  echo "  * Version: ${package_ver}"
+  echo "  * Dependencies: ${package_deps}"
+  echo -n "  * Installing..."
+  # Zero interaction while installing or upgrading the system via apt.
+  sudo DEBIAN_FRONTEND=noninteractive apt-get --yes install "${package}" > /dev/null
   echo "done."
 
-  echo -n "  Caching to $cache_filepath..."
-  # Pipe all package files (no folders) to Tar.
-  dpkg -L $package |
-    while IFS= read -r f; do     
-      if test -f $f; then echo ${f:1}; fi;  #${f:1} removes the leading slash that Tar disallows
-    done | 
-    xargs tar -czf $cache_filepath -C /    
-  echo "done."
+  for cache_package in "${package_deps}"; do
+    cache_filepath="${cache_dir}/${cache_package}.tar.gz"
+
+    if test ! -f "${cache_filepath}"; then
+      get_package_name_ver "${cache_package}" # -> package_name, package_ver      
+      echo -n "  Caching ${package_name} to ${cache_filepath}..."
+      # Pipe all package files (no folders) to Tar.
+      dpkg -L "${package_name}" |
+        while IFS= read -r f; do     
+          if test -f $f; then echo "${f:1}"; fi;  #${f:1} removes the leading slash that Tar disallows
+        done | 
+        xargs tar -czf "${cache_filepath}" -C /    
+      echo "done."
+      # Add package to manifest
+      manifest="${manifest}${package_name}:$(dpkg -s "${package_name}" | grep Version | awk '{print $2}'),"
+    fi
+  done
 done
 echo "done."
 
-manifest_filepath="$cache_dir/manifest.log"
-echo -n "Writing package manifest to $manifest_filepath..."
-manifest=
-for package in $packages; do
-  manifest=$manifest$package:$(dpkg -s $package | grep Version | awk '{print $2}'),
-done  
-# Remove trailing comma.
-echo ${manifest:0:-1} > $manifest_filepath
+manifest_filepath="${cache_dir}/manifest.log"
+echo -n "Writing package manifest to ${manifest_filepath}..."
+# Remove trailing comma and write to manifest file.
+echo "${manifest:0:-1}" > "${manifest_filepath}"
 echo "done."
\ No newline at end of file
diff --git a/lib.sh b/lib.sh
new file mode 100644
index 0000000..3802483
--- /dev/null
+++ b/lib.sh
@@ -0,0 +1,23 @@
+#!/bin/bash
+
+# Sort these packages by name and split on commas.
+function normalize_package_list {
+  stripped="$(echo \"${0}\" | sed 's/,//g')"
+  # Remove extraneous spaces at the middle, beginning, and end.
+  trimmed="$(echo \"${stripped}\" | sed 's/\s\+/ /g; s/^\s\+//g; s/\s\+$//g')"  
+  echo "$(\"${trimmed}\" | sort)"
+}
+
+# Split fully qualified package into name and version
+function get_package_name_ver {
+  IFS=\= read name ver <<< "${0}"
+  # If version not found in the fully qualified package value.
+  if test -z "${ver}"; then
+    ver="$(grep "Version:" <<< "$(apt show ${name})" | awk '{print $2}')"
+  fi
+  echo 'package_name="${name}"; package_ver="${ver}"'
+}
+
+function blah {
+  > /dev/null 2>&1
+}
\ No newline at end of file
diff --git a/pre_cache_action.sh b/pre_cache_action.sh
index ba09879..05d2fbe 100755
--- a/pre_cache_action.sh
+++ b/pre_cache_action.sh
@@ -1,5 +1,9 @@
 #!/bin/bash
 
+# Include library.
+script_dir="$(dirname -- "$(realpath -- "${0}")")"
+source "${script_dir}/lib.sh"
+
 # Directory that holds the cached packages.
 cache_dir=$1
 
@@ -7,34 +11,39 @@ cache_dir=$1
 version=$2
 
 # List of the packages to use.
-packages=${@:3}
+input_packages="${@:3}"
+
+# Trim commas, excess spaces, and sort.
+packages="$(normalize_package_list "${input_packages}")"
 
 # Create cache directory so artifacts can be saved.
 mkdir -p $cache_dir
 
 echo -n "Validating action arguments (version='$version', packages='$packages')...";
-echo $version | grep -o " " > /dev/null
-if [ $? -eq 0 ]; then
-  echo "aborted."
+if grep -q " " <<< "${cache_version}"; then
+  echo "aborted." 
   echo "Version value '$version' cannot contain spaces." >&2
   exit 1
 fi
-if [ "$packages" == "" ]; then
+
+# Is length of string zero?
+if test -z "${packages}"; then
   echo "aborted."
   echo "Packages argument cannot be empty." >&2
   exit 2
 fi
 echo "done."
 
+versioned_packages=""
 echo -n "Verifying packages..."
-for package in $packages; do
-  escaped=$(echo $package | sed 's/+/\\+/g')
-  apt-cache search ^$escaped$ | grep $package > /dev/null
-  if [ $? -ne 0 ]; then
+for package in ${packages}; do 
+  if test ! "$(apt show "${package}")"; then
     echo "aborted."
     echo "Package '$package' not found." >&2
     exit 3
   fi
+  get_package_name_ver "${package}" # -> package_name, package_ver  
+  versioned_packages="${versioned_packages} ${package_name}=${package_ver}"
 done
 echo "done."
 
@@ -43,15 +52,15 @@ set -e
 
 echo "Creating cache key..."
 
-# Remove package delimiters, sort (requires newline) and then convert back to inline list.
-normalized_list=$(echo $packages | sed 's/[\s,]+/ /g' | tr ' ' '\n' | sort | tr '\n' ' ')
-echo "- Normalized package list is '$normalized_list'."
+# TODO Can we prove this will happen again?
+normalized_versioned_packages="$(normalize_package_list "${versioned_packages}")"
+echo "- Normalized package list is '${normalized_versioned_packages}'."
 
-value=$(echo $normalized_list @ $version)
-echo "- Value to hash is '$value'."
+value="$(echo "${normalized_versioned_packages} @ ${cache_version}")"
+echo "- Value to hash is '${value}'."
 
-key=$(echo $value | md5sum | cut -f1 -d' ')
-echo "- Value hashed as '$key'."
+key="$(echo "${value}" | md5sum | /bin/cut -f1 -d' ')"
+echo "- Value hashed as '${key}'."
 
 echo "done."
 
diff --git a/restore_pkgs.sh b/restore_pkgs.sh
index ab87879..4c710f3 100755
--- a/restore_pkgs.sh
+++ b/restore_pkgs.sh
@@ -17,8 +17,8 @@ for cache_filepath in $cache_filepaths; do
 done
 
 echo "Reading from manifest..."
-for logline in $(cat $cache_dir/manifest.log | tr ',' '\n' ); do
-  echo "- $(echo $logline | tr ':' ' ')"
+for logline in "$(cat "${cache_dir}/manifest.log" | tr ',' '\n' )"; do
+  echo "- $(echo "${logline}" | tr ':' ' ')"
 done
 echo "done."